Class

Druid

Synergy · levels at 2 / 4 / 6 different pieces

Every Druid piece: When you make a ★★★ Druid, the remaining copies of that Druid are not removed from the shared pool.

Only different Druids on the board count. The 3-Wizard “unlock all levels” effect doesn't help Druid combining, because combining happens during preparation.

2
Two identical Druid★ combine into a Druid★★. An Io★ plus one Druid★ also combine.
4
Two identical Druid★★ combine into a Druid★★★. An Io★★ plus one Druid★★ also combine.
6
Two identical Druid★★★ combine into the Altar of Spirits. It gets Altar Power stacks equal to the Druid★★★'s level (5-8) and removes all Druids from the shared pool. Each stack means 10% less damage taken and 10% more damage dealt, multiplying (8 stacks: 43% damage taken, 214% damage dealt). At battle start the Altar shares its stacks with nearby friendly Druids it tethers.
Note: The tooltip suggests the Altar Power stacks add up; they multiply.

Official in-game tooltip

Druid pieces will not be destroyed on a ★★★ piece combined.

CLASS PERK: Synergy
Active when you have at least (N) different pieces of this class on board. (Multiple effects stack)

(2) Druids: Two identical Druid★ can promote to a Druid★★.
(4) Druids: Two identical Druid★★ can promote to a Druid★★★.
(6) Druids: Two identical Druid★★★ can promote to the great Altar of Spirits♥♥♥, and gain several(equal to the level of Druid★★★) stack of Altar Power, and destroy all Druid pieces in the chess pool.

Druids can control great power of Nature to protect spirits and balance.

Often paired with

Races and classes that Druid pieces also have, with how many share each.

Druid pieces (6)